Ajax :: Calling The Same Function For Each Onchange, Or Different Functions?

I'm trying to build a t-shirt creator application w/ php and ajax.You can see where I'm at here.Thus far, I've successfully passed the first parameter from the form via a function called from an onchange event, which uses a php script to pass simple text (for the time being, 'til i get this figured out), which you can see working on the page.trying to update the output w/ each change they make via the form. For every step, the output on the right needs to update.Should I be calling the same function for each onchange, or different functions? Here's what I'm using as far as AJAX/form goes:

Code:
function showShirt(s) {
// CHECKS IF THE STRING IS EMPTY
if (s=="") {[code]...........